The invention relates to a device comprising a sensor device with a detection device for determining information of at least a part of a surface of the sensor device, a display device comprising an electro-optical medium between two substrates, and a driver for driving the display device in dependence upon the information obtained via the detection device.
Devices of this type (also referred to as touch-panel displays) are generally known, in which different sensor mechanisms can be used. For determining information, it is possible to activate a part of the surface by scanning and measuring, for example activating via light (by means of, for example, a light pen) and by subsequently measuring induced currents or capacitively or resistively measuring electric voltages induced by pressure variation. The displayed information may vary from the co-ordinates of the part of the surface to the luminescence of the relevant part or possibly a menu activated thereby in computer applications.
A device of this type is described in U.S. Pat. No. 5,194,862. For the sensor device described in this patent it is indicated how it can be used as an overlay for a liquid crystal display device (LCD).
When this type of device is used, notably in portable applications (mini-notebook computers, personal digital assistance devices, telecommunication), it is desirable that a minimal quantity of energy is used. A considerable part of the energy is used in the illumination source which is situated behind the display device.
The device comprises, between the sensor device and the electro-optical medium, an optical guide of optically transparent material having a plurality of end faces, at least one of which is an entrance face for light, while light can be coupled in at said end face, and the side of the optical guide facing the electro-optical medium constitutes an exit face for the light. The substrate of the sensor device preferably comprises the optical guide.
Since the device and particularly the sensor device comprises the optical guide, the latter is. integrated therein and an illumination source (backlight) situated behind the electro-optical medium may be omitted. The entire device will thereby become more compact (flatter).
For a satisfactory coupling of the light from the optical guide to the electro-optical medium, the surface of the optical guide is preferably roughened or provided with a sawtooth structure or a substantially hemispheric structure on the side of the electro-optical medium.
The display device is preferably reflective. Such display devices make use of ambient light and are based on the use of a reflector or reflective electrodes. Since notably reflective LCDs are not sufficiently bright without the measure according to the invention in situations where there is little ambient light, transflective display devices (LCDs) are also used. In these devices, an illumination source (backlight) is situated behind the LCD while a transflector (transflective electrodes) is chosen instead of the reflector (the reflective electrodes). However, since the reflective power decreases, the optical quality of the image in the reflective mode is considerably reduced. Moreover, also in this case, it is necessary to arrange a backlight behind the electro-optical medium.
Another solution is the use of an extra light source at the front side (front light system). Here again, the total volume increases to such an extent that this is inadmissible, notably for said applications.
A preferred embodiment of a device according to the invention is characterized in that the substrate also comprises a substrate of the display device. The assembly will thereby become even more compact.
In a further embodiment, the substrate of the display device remote from the optical guide comprises a silicon substrate incorporating, for example, drive switches (active drive) or further drive functions.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.